Nonaqueous electrolyte secondary batteries, particularly lithium secondary batteries, have a high energy density, and are therefore in wide use as batteries for use in devices such as a personal computer, a mobile telephone, and a portable information terminal. Such lithium secondary batteries have recently been developed as on-vehicle batteries.
Patent Literature 1 discloses, as such a nonaqueous electrolyte secondary battery, a nonaqueous electrolyte secondary battery including a nonaqueous electrolyte secondary battery separator which contains a polyolefin porous film having a small amount of anisotropy of tan δ obtained by measurement of viscoelasticity.